This invention relates to a drive shield, and in particular to a drive shield which can be used for driving wide underground cavities, for example cavities used in the building of underground stations or their surrounding structures.
In order to drive tunnels, mine galleries and the like, it is known to use knife shields. A knife shield has a plurality of elongate planks (knives) supported side-by-side on a frame. The knives can be advanced either singly or in groups by means of hydraulic rams, there being a respective hydraulic ram associated with each knife. All the rams are mounted on the frame which acts as an abutment for the rams. When all the knives have been advanced, the frame is drawn up in a follow-up sequence by pressurising the rams in the opposite direction.
It is also known to form a wide cavity for receiving a concrete arched ceiling and tunnel walls by using a drive shield which consists of a plurality of knife shields which are arranged side-by-side tranversely of the direction of advance, the support frames of the shields being hinged to each other to form a chain. The disadvantage of such a drive shield is that the knives of some of the shields tend to retract as the frames are pulled up in the follow-up sequence.
The aim of the present invention is to provide a drive shield which can be used for driving wide underground cavities in an economical manner without the disadvantages of the known arrangements.